Sibyl married William de Ferrers III Fifth Earl of Derby, son of William de Ferrers Fourth Earl of Derby and Agnes de Keveliock Lady of Chartley. (William de Ferrers III Fifth Earl of Derby was born in 1193 in Derbyshire, England,1180 died on 28 Mar 1254 in Evington, Leicestershire, England 1180,1182 and was buried in Marevale Abbey, Warwickshire, England 1180.)